This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-351074, filed Nov. 17, 2000, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
This invention relates to an image forming apparatus which performs both sides printing by re-feeding paper on which image formation on one side thereof is finished by using an image formation mechanism for performing the image formation on one side of paper to the image formation mechanism after reversing the paper at a paper carry route, and by performing the image formation by using the image formation mechanism, and to a controlling method of paper carry at the image forming apparatus.
2. Description of the Related Art
Both sides printing by an electrophotographic apparatus and the like is realized by reversing paper on which image formation on one side thereof is finished and by re-feeding the paper to an image formation position by an image formation mechanism.
In such an image forming apparatus, a paper carry route becomes extremely long. Owing to this, if it is designed so as to perform printing on another sheet of paper after completing the both sides printing on one sheet of paper, a printing speed of the both sides printing becomes extremely slow.
Here, high-speed both sides printing can be realized by taking a design where plural sheets of paper can individually be carried in the paper carry route by providing plural motors. However, if plural motors are provided in this manner, cost of parts increases while a process burden of a CPU for controlling the motors increases since it becomes necessary to control more motors individually.
An object of the present invention is to enable high-speed both sides printing with a number of drive sources limited to the minimum.
According to an aspect of the invention, there is provided an image forming apparatus as below.
An image forming apparatus comprising;
an image formation mechanism which forms an image on a paper; a paper carry mechanism which carries the paper at a paper carry route having an image formation section which carries the paper toward one direction so as to make the image formation mechanism perform image formation on the paper, a return section which once takes in the paper carried out from the image formation section and carries out the paper toward a predetermined return direction being different from the direction toward the image formation section while reversing a carry direction, and a paper side reversal section which feeds the paper reversed to the other side after passing the image formation section at the last time to the image formation section at a predetermined timing after temporally stopping and holding the paper carried out from the return section; a drive source which rotates both a return roller provided in the paper carry mechanism in order to take in the paper carried out from the image formation section to the return section and to carry out the paper from the return section to the return direction, and at least one carry roller provided in the paper carry mechanism in order to carry the paper at the paper side reversal section; a clutch which transmits a driving force of the drive source to the carry roller having a possibility to nip and hold the paper when the paper is temporally stopped and held among the carry rollers only when the drive source is operating so that the return roller will carry the paper toward the return direction; and a carry control section which controls the paper carry by repeating a step of feeding the n-th sheet of paper on which the image formation on only one side is completed from the paper side reversal section to the image formation section, and feeding the n+1-th sheet of paper on which the image formation on only one side is completed from the return section to the paper side reversal section, and a step of, under the state where the n+1-th sheet of paper is held at the paper side reversal section, ejecting the n-th sheet of paper on which the image formation on both sides is completed, and feeding the n+2-th sheet of paper from the image formation section to the return section after taking-in the paper to the image formation area and performing the image formation on one side.
According to another aspect of the invention, there is provided a paper carry controlling method as below.
A paper carry controlling method in an image forming apparatus comprising;
an image formation mechanism which forms an image on a paper; a paper carry mechanism which carries the paper at a paper carry route having an image formation section which carries the paper toward one direction so as to make the image formation mechanism perform image formation on the paper, a return section which once takes in the paper carried out from the image formation section and carries out the paper toward a predetermined return direction being different from the direction toward the image formation section while reversing a carry direction, and a paper side reversal section which feeds the paper reversed to the other side after passing the image formation section at the last time to the image formation section at a predetermined timing after temporally stopping and holding the paper carried out from the return section; a drive source which rotates both a return roller provided in the paper carry mechanism in order to take in the paper carried out from the image formation section to the return section and to carry out the paper from the return section to the return direction, and at least one carry roller provided in the paper carry mechanism in order to carry the paper at the paper side reversal section; and a clutch which transmits a driving force of the drive source to the carry roller having a possibility to nip and hold the paper when the paper is temporally stopped and held among the carry rollers only when the drive source is operating so that the return roller will carry the paper toward the return direction, the paper carry controlling method being performed by repeating a step of feeding the n-th sheet of paper on which the image formation on only one side is completed from the paper side reversal section to the image formation section, and feeding the n+1-th sheet of paper on which the image formation on only one side is completed from the return section to the paper side reversal section, and a step of, under the state where the n+1-th sheet of paper is held at the paper side reversal section, ejecting the n-th sheet of paper on which the image formation on both sides is completed, and feeding the n+2-th sheet of paper from the image formation section to the return section after taking-in the paper to the image formation area and performing the image formation on one side.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.